Photographic products and processes utilizing inorganic chlorates as antifoggants



United States Iatent O 3,313,624 PHOTOGRAPHIC PRODUCTS AND PROCESSES UTILIZING INORGANIC CHLORATES AS AN- TIFOGGANTS Edwar B. Gutoif, Brookline, Mass, assignor to Polarold Corporation, Cambridge, Mass., a corporation of Delaware No Drawing. Filed July 17, 1963, Ser. No. 295,811 7 Claims. (Cl. 96-29) The present invention is concerned with photography and, more particularly, with novel photographic products and processes which utilize novel antifoggants and stabilizers.

One object of the present invention is to provide novel antifoggants and stabilizers.

Another object of the present invention is to provide novel antifoggants and stabilizers for silver halide emulsions which do not interfere with the speed or sensitivity of said emulsions.

A further object is to provide novel antifoggants and stabilizers which are useful in photosensitive elements particularly adapted for employment in diffusion transfer processes and especially in dye developer diffusion transfer processes.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

It is well known in the photographic art that light-sensitive silver halide emulsions, due to factors such as encountered during manufacture, storage and/or development, tend to fog. For this reason, it has been generally the practice to employ antifoggants or stabilizers to counteract this effect. Although various materials have been proposed for this purpose, it has been found that known antifoggants, in addition to reducing the fog have a tendency to adversely effect the speed of an associated emulsion.

It has now been found that such fog may be substantially reduced, without appreciably effecting the speed of the emulsions, by employing chlorate (C10?) salts as the antifoggants.

Generally, since the anion is the active portion of the salt, the cationic portions of the salt may be selected broadly from cations in general. Of course it will be understood that the use of cations having an adverse effect on emulsions will be avoided. In preferred embodiments, the cations are selected from among ammonia, the alkali metals and the alkaline earth metals.

Generally, the amount of chlorate salt employed may be varied depending on the fogging characteristics of the silver halide emulsion which is to be stabilized. In general, the use of about 0.1 to about 5 milligram equivalents (equivalent weight in milligrams) of the chlorates per gram of silver in the emulsion will effectively reduce fog. Particularly effective results were obtained using about 0.5 milligram equivalents of the salt per gram of silver.

The antifoggants of the present invention are particularly useful in silver and color diffusion transfer processes and, especially, in color dififusion transfer processes of the dye developer type.

Generally, in diffusion transfer processes an exposed silver halide emulsion is developed and, under the control 3,313,624 Patented Apr. 11, 1967 of the development, an imagewise distribution of imageforming components is formed which is transferred, at least in part, to a superposed image-receiving layer to form the transfer image thereon. In silver diffusion transfer processes, an exposed silver halide emulsion is developed with a silver halide developing agent in the presence of a silver halide solvent such, for example, as a thiosulfate or thiocyanate. Almost concurrently with the development of the latent image, the silver halide solvent reacts with the silver halide in unexposed and undeveloped areas to form a soluble, mobile silver complex. At least a portion of the silver complex is transferred to a print-receiving layer where it is precipitated to form the positive image. Suitable examples of such processes are disclosed in patents such as U.S. Patent No, 2,647,056 to Edwin H. Land.

Generally, in carrying out color diffusion transfer processes, a silver halide emulsion is exposed to create therein a latent image. The latent image is developed and concurrent with and under control of this development, an imagewise distribution of mobile color-providing materials, usually comprising one or more dyes or dye intermediates, is formed. At least a portion of these color-providing materials is transferred to a superposed image-receiving layer to form a colored positive image thereon. As examples of such processes, mention may be made of the processes disclosed and claimed in U.S. Patent No. 2,983,606, issued May 9, 1961 to Howard G. Rogers, wherein dye developers (i.e., compounds which are both dyes and silver halide developing agents) are the color-providing materials; the processes claimed and disclosed in U.S. Patent No. 2,647,- 049, issued July 28, 1953 to Edwin H. Land, wherein color developers are employed to develop the latent image and color couplers are the color-providing materials; and the processes disclosed in U.S. Patent No. 2,774,668, issued Dec. 18, 1956 to Howard G. Rogers, wherein complete, preformed dyes are used as the color-providing substances.

As pointed out above, the antifoggants of the present invention are especially useful in color diffusion transfer processes employing dye developers,- i.e., compounds which are both dyes and silver halide developing agents. Generally, in carrying out such processes, the dye developers are preferably disposed in the photosensitive element in a separate alkali-permeable layer contiguous with the silver halide emulsion layer. After exposure, the photosensitive element is permeated with an alkaline processing solution which solubilizes the dye developer. As a consequence of the development, the dye developer is immobilized in exposed areas. In unexposed and partial exposed areas of the emulsion the dye developer is unreacted and difiusible and thus provides an image-wise, mobile distribution of the dye developer. At least a portion of the imagewise distribution of the dye developer is transferred to a super posed image-receiving layer to form the positive image thereon.

Multicolor images may be obtained using color imageforming components such as, for example, the previouslymentioned dye developers, in diffusion transfer processes by several techniques. One such technique contemplates the use of a photosensitive silver halide stratum comprising at least two sets of selectively sensitized minute photosensitive elements arranged in the form of a photosensitive screen. Transfer processes of this type are disclosed in U.S. Patents Nos. 2,968,554 and 2,983,- 606. Another process for obtaining multicolor transfer images utilizing dye developers employs an integral multilayer photosensitive element, such as is disclosed in copending U.S. application Ser. No. 565,135, filed Feb. 13, 1966, wherein at least two selectively sensitized photosensitive strata are superposed on a single support and are processed, simultaneously and without separation, with a single, common image-receiving layer. A suitable arrangement of this type comprises a support carrying a red-sensitive silver halide emulsion stratum, a greensensitive silver halide emulsion stratum and a bluesensitive silver halide emulsion stratum, said emulsions having associated therewith, respectively, for example, a cyan dye developer, a magenta dye developer and a yellow dye developer. The dye developer may be utilized in the silver halide emulsion layer, for example, in the form of particles, or it may be employed as a layer behind the appropriate silver halide emulsion strata. Each set of silver halide emulsion and associated dye developer strata may be separated from other sets by suitable interlayers, for example, by a layer of gelatin or polyvinyl alcohol.

The chlorate salts may be effectively located in one or more silver halide emulsion layers and/or in adjacent layers of a film unit and/or in the processing solutions. Particularly efiective results have been obtained by incorporating the chlorates directly in the emulsion layers.

The following nonlimiting example illustrates the processes and products of the present invention.

Example A gelatin-coated film base was first coated with a 4% gelatin coating solution comprising sufficient 1,4-bis(amethyl [3 hydroquinonylethylamino) 5,8-dihydroxyanthraquinone (a cyan dye developer disclosed in the copending application of Blout et al., Ser. No. 233,461, filed Oct. 26, 1961) to give a coverage of about 100 to 110 milligrams per square foot. After this coating had dried, a silver iodobromide emulsion coating comprising about 230 to 250 milligrams of silver per square foot and 0.5 milligram equivalents (53.24 milligrams) of sodium chlorate per gram of silver was applied. The photosensitive element was then exposed and processed by spreading an aqueous liquid processing composition comprising:

Water cc 100 Sodium hydroxide grams 5.0 Hydroxyethyl cellulose do 4.03 Benzotriazole do 2.3 N-benzyl-ot-picolinium bromide do 2.3 Sodium thiosulfate do 1.15

between said photosensitive element and an imagereceiving element comprising a sheet of cellulose acetate subcoated baryta paper having coated thereon a mixture of polyvinyl alcohol and poly-4-vinylpyridine, as said elements were brought into superposed relationship. After an imbibition period of 2 minutes the image-receiving element may be separated to reveal a monochromatic reversed cyan dye image of the photographed subject.

The above procedure Was repeated with a control c011- taining no sodium chlorate. Fogs were taken on the element of the aboveexample and the control after imbibition periods of seconds and 2 minutes. The following comparative results were obtained:

Photosensitive IO-Seoond 2Minute Difiusion Element Fog Fog Transfer Exposure Index Control O. 70 1. 31 Sodium Chlorate 0. 40 0. 88 41 in a permeable layer adjacent the silver halide emulsion. In general, the most efificacious method has been determined to be that of directly disposing the chlorate salt in the silver halide emulsion. For example, the chlorate salt may be advantageously incorporated in the silver halide emulsion during the ripening or sensitivity increasing stage of the emulsion manufacturing process or as a coating final just prior to coating the emulsion on a suitable support.

It will be understood that silver halides of varying halide concentrations may be advantageously employed and that the silver halide emulsions employed may be chemically sensitized by any of the accepted procedures. For example, the emulsions may be chemically sensitized with sulfur compounds such as sodium thiosulfate or thiourea; with reducing substances such as stannous chloride; with salts of noble metals such as gold, rhodium and platinum; with amines and polyamines; with quaternary ammonium compounds such as u-picolinium bromide, etc.; and with polyethylene glycols and derivatives of same.

The emulsions may also be optically sensitized with cyanine and merocyanine dyes as described in US. Patents Nos. 1,846,301; 1,846,302; 1,942,854; 1,990,507; 2,112,140; 2,165,338; 2,493,747; 2,493,748; 2,503,776; 2,519,001; 2,666,761; 2,734,900; 2,739,964; etc.; and Where desired, suitable restrainers, accelerators, preservatives, coating aids, and/or additional stabilizers may be included in the composition of the emulsion.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrated and not in a limiting sense.

What is claimed is:

1.. A photosensitive silver halide emulsion comprising a chlorate salt, wherein the cation of said chlorate salt is selected from the group consisting of ammonium, alkali metals and alkaline earth metals.

2. A photosensitive silver halide emulsion as defined in claim 1, wherein said chlorate salt is present in a concentration of about 0.1 to about 5 milligram equivalents per gram of silver.

3. A photographic product which comprises a plurality of layers including a support, a silver halide gelatin emulsion located in a layer on said support, a dye developer in one of said layers on the same side of said support as the silver halide emulsion layer, said silver halide gelatin emulsion having associated therewith, in a layer on the same side of said support, a chlorate salt, said salt being present in a concentration of about 0.1 to about 5 milligram equivalents per gram of silver, wherein the cation of said chlorate salt is selected from the group consisting of ammonium, alkali metals and alkaline earth metals.

4. In a photographic process which comprises developing an exposed photosensitive element containing an exposed silver halide emulsion, the improvement which comprises conducting said process in the presence of a chlorate salt, wherein the cation of said chlorate salt is selected from the group consisting of ammonium, alkali metals and alkaline earth metals.

5. Ina diffusion transfer process which comprises the steps of developing an exposed photosensitive element containing a silver halide emulsion to form an imagewise distribution of image-forming components in said photosensitive element, and transferring, at least part of said imagewise distribution, by diffusion, to a superposed image-receiving layer to provide thereon a transfer image, the improvement which comprises conducting said process in the presence of a chlorate salt, wherein the cation of said chlorate salt is selected from the group consisting of ammonium, alkali metals and alkaline earth metals.

6. In a process for, forming diffusion transfer images in color which comprises the steps of developin an exposed silver halide emulsion in the presence of a dye, said dye being a silver halide developing agent, immobilizing said dye in the exposed areas as a result of development, forming thereby an imagewise distribution of mobile dye in unexposed areas, and transferring, by imbibition, at least a portion of said imagewise distribution of mobile dye to a superposed image-receiving layer to provide thereon a positive dye image, the improvement which comprises conducting said process in the presence of a chlorate salt, wherein the cation of said chlorate salt is selected from the group consisting of ammonium, alkali metals and alkaline earth metals.

References Cited by the Examiner UNITED STATES PATENTS 5/1961 Rogers 9629 12/1963 Sprung 96-109 10 NORMAN G. TORCHIN, Primary Examiner.

J. T. BROWN, Examiner. 

5. IN A DIFFUSION TRANSFER PROCESS WHICH COMPRISES THE STEPS OF DEVELOPING AN EXPOSED PHOTOSENSITIVE ELEMENT CONTAINING A SILVER HALIDE EMULSION TO FORM AN IMAGEWISE DISTRIBUTION OF IMAGE-FORMING COMPONENTS IN SAID PHOTOSENSITIVE ELEMENT, AND TRANSFERRING, AT LEAST PART OF SAID IMAGEWISE DISTRIBUTION, BY DIFFUSION, TO A SUPERPOSED IMAGE-RECEIVING LAYER TO PROVIDE THEREON A TRANSFER IMAGE, THE IMPROVEMENT WHICH COMPRISES CONDUCTING SAID PROCESS IN THE PRESENCE OF A CHLORATE SALT, WHEREIN THE CATION OF SAID CHLORATE SALT IS SELECTED FROM THE GROUP CONSISTING OF AMMONIUM, ALKALI METALS AND ALKALINE EARTH METALS. 